Immunosensing of Cardiac Troponin I (cTnI) Using a Two-Electrode Electrochemiluminescence Platform with Near Persisting Luminescence Generated on a Ru(bpy)32+-Tripropylamine System.

An economical, rapid, and ultrasensitive detection of biomolecules in clinical settings is very crucial, particularly for the early detection of Cardiac Troponin I (cTnI), which is the gold standard biomarker for Acute Myocardial Infarction (AMI). Electrochemiluminescence (ECL) has risen in prominence as an important technique for in vitro diagnosis and detection by virtue of its high sensitivity reaching a femtomolar level. This study introduces an economically feasible nanoplatform for ECL immunosensing, consisting of a gold nanoparticle (AuNP) with Ru(bpy)32+ and tripropylamine (TPA) system, which is a potential ECL luminophore and coreactant system. AuNPs serve the role of an ECL signal enhancer as well as the carrier of antibody, which enables the creation of a label-free immunosensor for antigen-antibody interactions. The prepared immunosensor detected cTnI with a detection limit (LOD) of 0.03 ng/mL. This potential immunosensor provides appreciable results in the detection of cTnI from spiked real serum analysis, which shows its potential application in low-resource clinical settings.

Exploring Selective Fluorescence Turn-On Sensing of Caspase-3 with Molybdenum Disulfide Quenched Copper Nanoclusters: FRET Biosensor.

Sensing caspase-3 activity is essential for understanding the role of apoptosis in cancer dynamics, controlling therapeutic strategies, and improving patient care in cancer treatment. In this study, we demonstrate a highly sensitive recombinant human caspase-3 (rhC3) detection technique in biological fluids. This technique uses a copper nanocluster stabilized with bovine serum albumin (BSA-CuNCs) as a metal-based fluorescent biosensor, conjugated with anti-human caspase-3 (ahC3). To turn its fluorescence off, molybdenum disulfide nanosheets (MoS2 NSs) are added; this partnership is termed ahC3@BSA-CuNCs/MoS2 nanocouple. In the presence of rhC3, the energy transfer process is affected by strong ahC3/rhC3 interactions. When in close proximity, the rhC3 molecules cause detachment of the nanocluster from the MoS2 NS surface by attracting the ahC3 component of the nanocluster. This increases the distance between the nanocluster and quencher with a consequent restoration of intensity. As the concentration of rhC3 increases, the fluorescence intensity of the system also increases. A proportional response is seen in the concentration between 0.1 and 1.3 ng/mL with a very low limit of detection of 2.75 pg/mL and a quantification limit of 8.60 pg/mL. A simple filter paper strip was made to visually identify the presence of rhC3 under UV light.

Impregnation of two-dimensional manganese dioxide nanosheets with 5-carboxyfluorescein as an immunoassay platform for sensitive detection of cardiac troponin T.

A novel immunoassay platform is presented utilizing a cardiac troponin T antibody (Ab-cTnT) labelled with 5-carboxyfluorescein (5-FAM) integrated into a two-dimensional (2D) manganese dioxide nanosheet (MnO2 NS) matrix. This strategy enables a turn-on response towards cTnT antigen within a mere 10-min incubation period, boasting an impressive lower detection limit of 0.038 ng/mL. Crucially, our probe demonstrates exceptional selectivity amidst the presence of coexisting biomolecules and ions, ensuring precise detection of cTnT. Moreover, the developed platform showcases promising utility in sensing cTnT from spiked human serum samples, yielding satisfactory recovery percentages ranging from 82 to 105%. Additionally, we introduce and easy-to-use and cost-effective test strip for point-of-care detection of cTnT, further enhancing accessibility to critical cardiovascular diagnostics.

Fluorescence anisotropic probe for sensing cardiac troponin-I antigen through target-specific antibody-conjugated gold nanoclusters.

Fluorescence anisotropy (FA) is a versatile and efficient platform for developing biosensors that rely on the rate of rotations of fluorescence molecular entities in biochemical systems. However, by virtue of its intricate complexity, FA is a neglected and less explored area for developing biosensors. Herein, we experimented with the possibility of developing a fluorescence anisotropic probe to detect cardiac troponin I (cTnI), the gold standard biomarker for acute myocardial infarction, via target-specific monoclonal antibody-conjugated gold nanoclusters. The successful detection of cTnI antigen in clinically relevant concentration with a low detection limit of 0.91 ng mL-1 was achieved. The specific molecular interaction between the cTnI antigen and its monoclonal antibody tagged at the surface of gold nanoclusters has restricted the free rotation of gold nanoclusters and increased the FA value. This incremental increase in FA can be correlated to the concentration of cTnI antigen in the sample, thereby achieving the quantitative linear detection of cTnI.

Luminescence "Turn-On" Sensing of Brain Natriuretic Peptide (BNP) - Dilated Cardiomyopathy Biomarker Based on the MoS2 Nanosheet Quenched Terbium Citrate Complex.

Dilated cardiomyopathy (DCM), known as myocardial metabolic dysfunction, is recognized as a clinical condition characterized by left ventricular dilation or improper contraction of cardiac muscles in the absence of coronary atherosclerosis and hypertension. It is an independent risk factor for cardiac function caused by a hyperglycemic condition in diabetic patients leading to heart failure (HF), which renders the early diagnosis of DCM highly challenging. Hence, detection of early diagnostic biomarkers in blood serum to identify DCM conditions is quite requisite. Brain natriuretic peptide (BNP) is a well-recognized biomarker for heart failure and reported as an early diagnostic biomarker for DCM. In this work, we developed a terbium citrate based MoS2 nanosheet (NS) coupled immunoprobe for the sensitive detection of BNP. The antibody conjugated Tb-citrate complex exhibits green fluorescence, which is quenched by the introduction of MoS2 NS. On subsequent addition of antigen BNP, the fluorescence is enhanced because of specific antigen-antibody interaction. The probe is selective and sensitive toward BNP in a linear range from 30.76 to 849.85 pg/mL with a low LOD of 3.87 pg/mL. The probe is validated in spiked human serum samples with good recovery percentage.

Non-Enzymatic Detection of Cardiac Troponin-I with Graphene Oxide Quenched Fluorescent Iron Nanoclusters (FeNCs).

Cardiac troponin I (cTnI) is the most resorted biomarker for the detection of cardiovascular disease (CVD). The means of rapid quantification of cTnI levels in the blood can substantially minimize the risk of acute myocardial infarction and heart failure. A sensor for the non-enzymatic evaluation of cardiac troponin-I has been developed using fluorescent iron nanoclusters via a one-pot synthesis employing (BSA) as the template and reducing agent, and hydrogen peroxide as the additive. The fluorescence of Iron Nanocluster is quenched with graphene oxide (GO) via fluorescence resonance energy transfer (FRET) between conjugate iron nanoclusters and graphene oxide. The sensor shows a low detection limit of 0.011 ng/mL. The benefits of utilizing a non-enzymatic probe for detecting cardiac troponin I is that it avoids the need for enzymes and hence is economical, stable, and less impacted by environmental conditions such as temperature and pH. Non-enzymatic probes are more useful for clinical use since they are more stable and have a longer shelf life. The developed non-enzymatic probes are also highly selective and sensitive to the target analyte, making them suitable for the direct detection of cardiac troponin I in actual biological samples.

Mo(IV) Ion-Modulated BSA-Protected Gold Nanocluster Probe for Fluorescence Turn-On Detection of Trimethylamine N-Oxide (TMAO).

Trimethylamine N-oxide (TMAO), a molecule produced by the microbiota, has been associated with human health and illness. Its early discovery in body fluids may affect our understanding of the pathophysiology and treatment of many illnesses. Therefore, our knowledge of the pathophysiology and diagnostics of disorders associated with TMAO might be enhanced by the creation of dependable and fast methods for TMAO detection. Therefore, we developed a fluorescent probe for detecting TMAO utilizing an on-off-on strategy. Bovine serum albumin (BSA)@AuNCs luminescence is effectively quenched by Mo4+ because BSA@AuNCs and Mo4+ have a strong binding relationship. Mo4+ ions can substantially decrease the emission intensity of gold nanoclusters by establishing a BSA@AuNCs-Mo system. Then, the luminescence of BSA@AuNCs was restored due to the interaction between Mo4+ and TMAO. A significant linear relationship was seen between the emission intensity and TMAO concentration within the 0-201 µM range, with a detection limit of 1.532 µM. Additionally, the method can measure TMAO in blood and urine samples.

Efficient nanostructured Cs2CuBr2Cl2 perovskite as a fluorescent sensor for the selective "Switch Off" detection of nitrobenzene.

Lead halide nanostructured perovskites are well known for their excellent photoluminescence and optoelectronic properties. However, lead toxicity and instability in moisture impedes its suitability for material use. Here we synthesized a highly efficient, lead free, economical, stable Cs2CuBr2Cl2 perovskite nanocrystals (PNCs) via Ligand Assisted Re-Precipitation (LARP) method which is less explored. The sensing application of the synthesized PNCs towards nitro explosives and other small organic compounds were studied. The probe exhibited high selectivity towards nitrobenzene with a lowest detection limit of 57.64 nM. The fluorescent emission intensity was drastically quenched upon the addition of 32 µM nitrobenzene. A Stern-Volmer plot was utilized for the quantification of fluorescence quenching. Further to investigate the quenching mechanism, time correlated single photon counting spectroscopy and other photoluminescence studies were performed pointing out the possibility of fluorescence resonance energy transfer. The work has been further extended to test the capability of the probe to detect nitrobenzene in real water samples and a good recovery percentage ranging from 93-98 % was obtained. Further, a paper strip assay was designed which successfully detected nitrobenzene and can be clearly noticed even with our naked eye making the probe an excellent sensor for nitrobenzene detection.

Terbium Phenanthroline Complex as a Luminescent Probe for the Detection of Anthrax Biomarker: Dipicolinic acid.

Dipicolinic acid (DPA) is a prominent biomarker for Anthrax disease. Bacillus anthracis bacterial endospores is composed of DPA as the significant component, which on over inhalation can cause severe health issues. Such contagious and life-threatening pathogens can be employed as bioweapons or biothreat agents for spreading bioterrorism which is a major risk for national security and public health concerns. Hence, effective detection or a surveillance system is essential for preventing the growth of bioterrorism events. Herein, we have developed a Terbium - 1,10 Phenanthroline (Tb-Phen) based lanthanide luminescence complex with bright green fluorescence. On addition of DPA, the green fluorescence is turn-off at a linear range from 0.6 to 4.762 mM. In this effect, 5D4- 7F5 transition caused by 1,10-phenanthroline to Tb3+ at 544 nm is restricted due to energy transfer quenching and Inner Filter Effect (IFE). The developed probe shows good sensitivity towards the detection of DPA with other coexisting biomolecules and ions with a low Limit of Detection (LOD) of 5.029 µM. The practical feasibility was evaluated in paper strip assay and extended in real samples such as human serum and tap water with satisfactory recovery percentage. Thereby, probe finds promising application in sensing of anthrax spore biomarker (DPA) and biothreat agents.

MnO2 nanosheet quenched thulium doped photon-up conversion luminescent immunoprobe for the 'turn-on' detection of cardiac troponin T.

A "turn-on" photon up conversion nano couple based on NaYF4: Yb, Tm UCNPs quenched with MnO2 nanosheet was developed for the rapid and selective detection of cTnT. Herein, MnO2 nanosheet hold on the surface of Antibody cTnT (Ab-cTnT) conjugated blue emitting up conversion nanoprobe (λem at 475 nm), which leads to quenching of fluorescence due to energy transfer from photon up conversion nanoparticles to MnO2 nanosheets. On introducing cTnT antigen to the system, the energy transfer process is hindered due to strong antigen -antibody interface on the surface. This in turn, influences the nano-couples positions and effectively separates up conversion nanoprobe from MnO2 nanosheets surface resulting in restriction to energy transfer process enabling fluorescence recovery. The developed probe shows a linear response towards cTnT in the range of 0.16-2.77 ng/mL with a Limit of Detection (LoD) of 0.025 ng/mL. The practical feasibility of the nanoprobe is performed with possible coexisting biomolecules. Biological study in human blood serum samples exhibited sufficient recovery percentage in the range of 92-103 % is obtained.

Highly sensitive lanthanide complex as a probe for l-kynurenine: A cancer biomarker.

A lanthanide complex based on europium (Eu) and chelidamic acid was synthesized (Eu-CHE) and characterized. The complex Eu-CHE exhibited intense luminescence at 615 nm under excitation at 300 nm and was further investigated for highly sensitive turn-off detection of l-kynurenine (l-kyn), a cancer biomarker. The probe detected l-kyn linearly from 6 nM to 0.2 µM with a limit of detection and limit of quantification of 1.37 and 4.57 nM, respectively. The probe was investigated for selectivity towards l-kyn among co-existing amino acids and further extended for detecting l-kyn from human serum and urine samples. A low-cost paper strip-based sensing platform was also developed for the visual detection of l-kyn.

Fluorescent Enzymatic Sensor Based Glucose Oxidase Modified Bovine Serum Albumin-Gold Nanoclusters for Detection of Glucose.

An enzymatic fluorescent probe is developed for the selective detection of glucose. In this work, a Bovine Serum Albumin stabilized gold nanocluster (BSA-AuNCs) was synthesized by microwave assisted method, and it is modified with glucose oxidase, thereby a fluorescent enzymatic sensor (BSA-AuNCs@GoX) was designed for the sensitive detection of glucose with a limit of detection of 0.03 mM. The red fluorescence exhibited by the probe is quenched by the production of H2O2 on addition of glucose via. a static quenching mechanism from UV visible absorption and Fluorescence lifetime results. The developed probe exhibits good selectivity and sensitivity with other coexisting molecular species such as glycine, creatinine, methionine, histidine, uric acid, albumin, and ions such as sodium, potassium, calcium, magnesium, zinc etc. that appear in the body fluid. The practical applicability was studied in paper strip and extended its reproducibility in biological matrixes such as human serum and urine and found a good recovery percentage of 94-101 %. By this way, we have fabricated an effective fluorescent enzymatic "turn-off" sensing probe for the detection of glucose.

L-Methionine and D-Methionine Capped Fluorescent Silicon Quantum Dots Based Probes for Turn on Sensing of Glutathione - A Comparative Study.

Oral Squamous Cell Carcinoma (OSCC), a prevalent type of oral cancer originates in squamous cells that develop due to tobacco use, excess alcohol consumption, human papillomavirus infection, chronic irritation and weakened immune system. When detected early, survival rates of OSCC can be increased to more than 85%. Hence its early detection is crucial for appropriate management. Oxidative stress has a vital role in pathogenesis of various cancers including OSCC. Early detection of OSCC can be done by exploring serum Glutathione (GSH); an oxidative stress biomarker. Herein, we have developed two Silicon quantum dots (SiQDs); (L-methionine capped Silicon quantum dots (LSiQDs) and D-methionine capped Silicon quantum dots (DSiQDs)) and their fluorescence was quenched with Cu2+. The obtained Cu@LSiQDs and Cu@DSiQDs were then explored and compared for sensing GSH. Both the SiQDs were checked for selectivity and interference studies using coexisting biomolecules extended for sensing GSH from real samples. Moreover, a paper strip assay was also developed and compared.

NaYF4:Yb/Ho upconversion nanoprobe incorporated gold nanoparticle (AuNP) based FRET immunosensor for the "turn-on" detection of cardiac troponin I.

Cardiac troponin I (cTnI) is a significant biomarker for acute heart attack. Hence, fast, economical, easy and real time monitoring of cardiac troponin I (cTnI) is of great importance in diagnosis and prognosis of heart failure in the healthcare domain. In this work, an immunoassay based on NaYF4:Yb/Ho based photon-upconversion nanoparticle (UCNP) with narrow emission peaks at 540 nm and 655 nm respectively, is synthesized. Then, it is encapsulated with amino functionalized silica using 3-aminopropyltriethoxysilane (APTES) to form APTES@SiO2-NaYF4:Yb/Ho UCNPs. When AuNPs is added to this system, the fluorescence is quenched by the electrostatic interaction with APTES@SiO2-NaYF4:Yb/Ho UCNPs, thereby exhibiting a FRET-based biosensor. When the cTnI antigen is introduced into the developed probe, an antibody-antigen complex is formed on the surface of the UCNPs resulting in fluorescence recovery. The developed sensor shows a linear response towards cTnI in the range from 0.1693 ng mL-1 to 1.9 ng mL-1 with a low limit of detection (LOD) of 5.5 × 10-2 ng mL-1. The probe exhibits adequate selectivity and sensitivity when compared with coexisting cardiac biomarkers, biomolecules and in real human serum samples.